/*

 * Copyright (c) 2014, Oracle America, Inc.

 * All rights reserved.

 *

 * Redistribution and use in source and binary forms, with or without

 * modification, are permitted provided that the following conditions are met:

 *

 *  * Redistributions of source code must retain the above copyright notice,

 *    this list of conditions and the following disclaimer.

 *

 *  * Redistributions in binary form must reproduce the above copyright

 *    notice, this list of conditions and the following disclaimer in the

 *    documentation and/or other materials provided with the distribution.

 *

 *  * Neither the name of Oracle nor the names of its contributors may be used

 *    to endorse or promote products derived from this software without

 *    specific prior written permission.

 *

 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"

 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE

 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE

 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE

 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR

 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF

 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS

 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN

 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)

 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF

 * THE POSSIBILITY OF SUCH DAMAGE.

 */

package org.openjdk.jmh.samples;


import org.openjdk.jmh.annotations.*;

import org.openjdk.jmh.runner.Runner;

import org.openjdk.jmh.runner.RunnerException;

import org.openjdk.jmh.runner.options.Options;

import org.openjdk.jmh.runner.options.OptionsBuilder;


import java.util.concurrent.TimeUnit;


@State(Scope.Thread)

@BenchmarkMode(Mode.AverageTime)

@OutputTimeUnit(TimeUnit.NANOSECONDS)

public class JMHSample_11_Loops {


 /*

  * It would be tempting for users to do loops within the benchmarked method.

  * (This is the bad thing Caliper taught everyone). These tests explain why

  * this is a bad idea.

  *

  * Looping is done in the hope of minimizing the overhead of calling the

  * test method, by doing the operations inside the loop instead of inside

  * the method call. Don't buy this argument; you will see there is more

  * magic happening when we allow optimizers to merge the loop iterations.

  */


 /*

  * Suppose we want to measure how much it takes to sum two integers:

  */


 int x = 1;

 int y = 2;


 /*

  * This is what you do with JMH.

  */


 @Benchmark

 public int measureRight() {

  return (x + y);

 }


 /*

  * The following tests emulate the naive looping.

  * This is the Caliper-style benchmark.

  */

 private int reps(int reps) {

  int s = 0;

  for (int i = 0; i < reps; i++) {

   s += (x + y);

  }

  return s;

 }


 /*

  * We would like to measure this with different repetitions count.

  * Special annotation is used to get the individual operation cost.

  */


 @Benchmark

 @OperationsPerInvocation(1)

 public int measureWrong_1() {

  return reps(1);

 }


 @Benchmark

 @OperationsPerInvocation(10)

 public int measureWrong_10() {

  return reps(10);

 }


 @Benchmark

 @OperationsPerInvocation(100)

 public int measureWrong_100() {

  return reps(100);

 }


 @Benchmark

 @OperationsPerInvocation(1_000)

 public int measureWrong_1000() {

  return reps(1_000);

 }


 @Benchmark

 @OperationsPerInvocation(10_000)

 public int measureWrong_10000() {

  return reps(10_000);

 }


 @Benchmark

 @OperationsPerInvocation(100_000)

 public int measureWrong_100000() {

  return reps(100_000);

 }


 /*

  * ============================== HOW TO RUN THIS TEST: ====================================

  *

  * You might notice the larger the repetitions count, the lower the "perceived"

  * cost of the operation being measured. Up to the point we do each addition with 1/20 ns,

  * well beyond what hardware can actually do.

  *

  * This happens because the loop is heavily unrolled/pipelined, and the operation

  * to be measured is hoisted from the loop. Morale: don't overuse loops, rely on JMH

  * to get the measurement right.

  *

  * You can run this test:

  *

  * a) Via the command line:

  *    $ mvn clean install

  *    $ java -jar target/benchmarks.jar JMHSample_11 -f 1

  *    (we requested single fork; there are also other options, see -h)

  *

  * b) Via the Java API:

  *    (see the JMH homepage for possible caveats when running from IDE:

  *      http://openjdk.java.net/projects/code-tools/jmh/)

  */


 public static void main(String[] args) throws RunnerException {

  Options opt = new OptionsBuilder()

          .include(JMHSample_11_Loops.class.getSimpleName())

          .forks(1)

          .build();


  new Runner(opt).run();

 }
// 本例直接给出一个结论，不要在基准测试的时候使用循环，使用循环就会导致测试结果不准确，原因很复杂，甚至可以单独写一篇文章来介绍。简单能理解的一点是如果使用循环，预热可能就会存在问题。

}